'\"
'\" Copyright (c) 2006-2008 Joe Mistachkin.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH Tcl_Cancel 3 8.6 Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_CancelEval, Tcl_Canceled \- cancel Tcl scripts
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
int
\fBTcl_CancelEval\fR(\fIinterp, resultObjPtr, clientData, flags\fR)
.sp
int
\fBTcl_Canceled\fR(\fIinterp, flags\fR)
.SH ARGUMENTS
.AS Tcl_Interp *interp
.AP Tcl_Interp *interp in
Interpreter in which to cancel the script.
.AP Tcl_Obj *resultObjPtr in
Error message to use in the cancellation, or NULL to use a default message. If
not NULL, this object will have its reference count decremented before
\fBTcl_CancelEval\fR returns.
.AP int flags in
ORed combination of flag bits that specify additional options.
For \fBTcl_CancelEval\fR, only \fBTCL_CANCEL_UNWIND\fR is currently
supported.  For \fBTcl_Canceled\fR, only \fBTCL_LEAVE_ERR_MSG\fR and
\fBTCL_CANCEL_UNWIND\fR are currently supported.
.AP ClientData clientData in
Currently reserved for future use.
It should be set to NULL.
.BE
.SH DESCRIPTION
.PP
\fBTcl_CancelEval\fR cancels or unwinds the script in progress soon after
the next invocation of asynchronous handlers, causing \fBTCL_ERROR\fR to be
the return code for that script.  This function is thread-safe and may be
called from any thread in the process.
.PP
\fBTcl_Canceled\fR checks if the script in progress has been canceled and
returns \fBTCL_ERROR\fR if it has.  Otherwise, \fBTCL_OK\fR is returned.
Extensions can use this function to check to see if they should abort a long
running command.  This function is thread sensitive and may only be called
from the thread the interpreter was created in.
.SS "FLAG BITS"
Any ORed combination of the following values may be used for the
\fIflags\fR argument to procedures such as \fBTcl_CancelEval\fR:
.TP 20
\fBTCL_CANCEL_UNWIND\fR
.
This flag is used by \fBTcl_CancelEval\fR and \fBTcl_Canceled\fR.
For \fBTcl_CancelEval\fR, if this flag is set, the script in progress
is canceled and the evaluation stack for the interpreter is unwound.
For \fBTcl_Canceled\fR, if this flag is set, the script in progress
is considered to be canceled only if the evaluation stack for the
interpreter is being unwound.
.TP 20
\fBTCL_LEAVE_ERR_MSG\fR
.
This flag is only used by \fBTcl_Canceled\fR; it is ignored by
other procedures.  If an error is returned and this bit is set in
\fIflags\fR, then an error message will be left in the interpreter's
result, where it can be retrieved with \fBTcl_GetObjResult\fR or
\fBTcl_GetStringResult\fR.  If this flag bit is not set then no error
message is left and the interpreter's result will not be modified.
.SH "SEE ALSO"
interp(n), Tcl_Eval(3),
TIP 285
.SH KEYWORDS
cancel, unwind
